The present invention relates to a process and apparatus for the disinfection of seeds. This process offers advantageous handling of grain in high volume and is adapted for disinfection of the surface and the near surface layers of the seed, which can become or are infected with seed-borne pathogens. Seeds, especially grains, therefore, are to be disinfected before use. Such a disinfection is prescribed by law in many countries.
It is well known that the surfaces of seeds which may be or are attacked by seed pathogens can be disinfected with chemical substances prior to sowing.
To date, such chemical substances have been biocidals based either on heavy metals, such as aryl mercury or alkyl compounds, or on organic compounds free from heavy metals, that is, fungicides. The mercury-containing disinfecting agents have wide-reaching fungicidal effects on the pathogens without causing resistance phenomena, but also have the distinct disadvantage of exceptional toxicity. Thus the use of these materials requires special efforts to protect individuals involved in the disinfection and sowing because any careless handling of the grain so treated presents a specific hazard to man, animals and the environment. In accordance with World Health Organization regulations, no mercury-containing disinfectant compounds can be used. It was methyl mercury, of course, that caused the infamous "Minimata disease" in Japan.
Mercury-free chemical disinfectants which came out after those regulations have a lot of disadvantages compared with disinfectants containing the mercury compounds. For attaining a required universal effect, combined preparations including several substances are necessary, which results in up to a 15 to 20-fold price increase for treatment. Aside from some technological problems, their broad application can cause a build-up of immunity in some organisms. Also, several disinfectants retard germination of crops, while others have a smaller specific weight and, thus, a greater volume which impairs adherence on the seeds. In some cases, toxic and carcinogenic effects on man cannot be excluded with certainty.
In addition to disinfection by chemical processes, there are physical processes which are also known. These essentially consist of the application of steam for heating up the seeds to a temperature critical for the pathogens, as well as applications of light, microwaves or ions. Such physical processes are limited to special conditions and have proven unsuitable for large scale agricultural use.
The application of high-energy ionizing radiation in the MeV range leads to the complete exposure of the seed by transmission of the radiation therethrough. This is used for growth stimulation of crops and for disinfection of feed grains. The radiation dose selected for the first case are very low, and are in the range of a few hundred Rads. If one exceeds the growth-stimulating radiation doses, the radiation has mutagenic or phytotoxic effect. The radiation dose needed for disinfection is at least a factor of 10.sup.3 above the dose needed to stimulate plate growth and kills the embryo in the seed as a consequence. Thus, irradiation with high-energy ionizing radiation for disinfection is out of the question.